One of the reasons the US keeps "blustering" about N. Korea is S. Korea and Japan are extremely worried about a nuclear armed N. Korea. Likely because N. Korea

One of the reasons the US keeps "blustering" about N. Korea is S. Korea and Japan are extremely worried about a nuclear armed N. Korea. Likely because N. Korea has been conducting low level military actions against them over the last 50 years, abducting and killing civilians, firing artillery barrages, attacking and sinking military ships, all with the intent of blackmailing ransom payments. Now N. Korea can only go so far with artillery barrages or sinking military ships before they face military retaliation. But once they are nuclear armed, they could bombard the suburbs of Seoul until a ransom was paid. Without fear of retaliation. Because they've already made it quite clear they really want to use their nuclear weapons, so pay up or get nuked. So if the US backed off, S. Korea, Japan and likely every other country in the region would immediately acquire nuclear weapons. And either N. Korea stops its blackmail programs or a nuclear war breaks out.